Graticule
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A graticule is a network of geographic lines. We use it to refer to the rectangular zones between the latitude and longitude lines, each 1°×1° in size.
Shape
The shape and size of a graticule as measured over the ground (in miles or kilometers) varies with distance from the equator. A graticule near the equator (latitude 0) is almost exactly square shaped (roughly 111×111 km or about 69×69 miles); other graticules are still 111 km in north-south direction, but become narrower and narrower as one goes further away from the equator. For example, the Groningen graticule, at +53° latitude, is roughly 67 km in the east-west direction. Graticules touching on the North Pole (or the South Pole) actually have the shape of a piece of pie, since the northern (southern) border of such a graticule has length 0. Google maps, however, does not cover latitudes below -85° or above +85°.
Numbering
Graticules are numbered based on the corner closest to N0°, E0° such that the graticule a location belongs to can be determined by truncating the degree fraction.